The present invention relates to a method and a device for adjusting the sensitivity of a device for detecting foreign objects in an agricultural harvesting machine.
Agricultural harvesting machines are subjected to enormous stresses during the harvesting operation. For example, all working assemblies on a self-propelled field chopper, e.g., the cutting mechanism, pre-compression rollers or the chopping drum, are subjected to enormous stresses by the crop material to be processed. Foreign objects, such as stones or branches, located on the ground pose particular problems. Stones, in particular, are drawn up by the cutting mechanism along with the crop material and are conveyed by the pre-compression rollers to the downstream chopping drum. This often causes serious damage to the chopping knives located on the chopper drum and, as a result, the harvesting operation must be interrupted and the damaged chopping knives must be replaced, which is a time-consuming, expensive operation.
Publication EP 0 217 418 B1 discloses a foreign-object detection device for agricultural harvesting machines, a movable accelerometer being assigned to a movable feed device and being located perpendicular to the feed direction of the crop material strand. The direction in which measurements are carried out by the acceleration sensor is the direction in which the movable part of the feed device is displaced by the moving stream of crop material. A threshold value for a predefinable, maximum permissible acceleration of the deflection of the movable part of the feed device is specified in a data recording and evaluation unit. If it is determined that the actual acceleration of deflection of the movable part of the feed device exceeds the threshold value, a quick stop is triggered and all working assemblies in the agricultural harvesting machine are brought to a standstill.
The disadvantage of the design disclosed in publication EP 0 217 418 B1 is the fact that rapid deflections can also be caused when large quantities of crop material are drawn in, thereby resulting in an unnecessary triggering of a quick stop. In addition, the driver of the agricultural harvesting machine is unable to respond to changes caused by the crop material. It is not possible to quickly adjust the acceleration threshold value to the current harvesting requirements. An adjustment is required, e.g., when a different type of crop is harvested. For instance, the compressibility of grass is different from that of corn; as such, the movable part of the feed device is deflected to a different extent by different types of crop material. In particular, when processing grass which was set down on the field in a swath, the feed device undergoes considerable fluctuations in terms of deflection, since the swath is often unevenly shaped and grass tends to form grass clumps that stick together.